The impact of hematite on the anaerobic digestion of cattle manure

Abstract

A metal-based conductive material, hematite (Fe2O3), was used as an amendment in the anaerobic digestion process to determine the effects on the performance of anaerobic digestion of cattle manure (CM) at mesophilic temperature (350C). The first set of experiments (Set 1) was designed to assess whether there is a need to supplement nutrients for the effective digestion of CM. To this purpose, basal medium (BM) composed of macro nutrients, micro nutrients, reducing agent, and buffer was added to the reactors and a biochemical methane production assay was conducted. The presence of BM showed negative impacts on the anaerobic digestion of CM and its absence caused up to 40% higher methane production yield. In Set 2 experiments, the impact of hematite addition on methane production performance was determined. Two different dosages as 20 mM Fe (Fe20) and 50 mM Fe (Fe50) were applied to the batch reactors. Hematite amendments increased methane yield; at Fe20 (131 ± 2.6 mL CH4/g VSadded) the increase was around 8% and at Fe50 (135 ± mL 0.2 CH4/g VSadded) the increase was around 12% as compared to the control. Further, up to 36% increase in the methane production rate was calculated via Modified Gompertz fitting.